Ex-Colombian president Álvaro Uribe. His niece and her mother are accused of having ties to the head of Mexico's Sinaloa drugs cartel. Photograph: Fernando Vergara/AP

A niece of the former Colombian president Álvaro Uribe has been singled out by US officials as having ties to a drug trafficking clan while her mother awaits extradition to the US over claims she worked together with the world most wanted drug trafficker.

Dolly Cifuentes Villa was arrested last year after a request from a US federal court for alleged ties to the head of Mexico's Sinaloa Cartel, Joaquín "El Chapo" Guzmán. Her daughter Ana Maria Uribe Cifuentes was recently placed on the US Treasury's list of people identified as acting on behalf of drug trafficking or terrorist organizations.

According to an investigation published by the Nuevo Arco Iris political research centre in Bogotá, Uribe Cifuentes is the daughter of former president Álvaro Uribe's brother Jaime, who died of throat cancer in 2001.

Both women are alleged to belong to the Cifuentes Villa clan which, according to the Drug Enforcement Administration, trafficked at least 30 tonnes of cocaine to the US between 2009 and 2011, and laundered the proceeds in several Latin American countries including Colombia.

On Friday, Colombian police announced they had seized US$15m (£10m) in assets from the Sinaloa cartel, owned by Cifuentes Villa and two of her brothers on behalf of El Chapo.

On Sunday, Álvaro Uribe denied any knowledge of Jaime's relationship with Cifuentes Villa, or the existence of his niece, despite the fact the investigation has a fax of a birth certificate declaring Jaime Uribe as her father.

"My brother Jaime died in 2001, married to Astrid Velez, they had two children ... Any other romantic relationship that my brother may have had was part of his personal life and is unknown to me," Álvaro Uribe tweeted on Sunday. He denied Jaime was ever linked to the drug lord Pablo Escobar.

According to the Nuevo Arco Iris investigation, Jaime Uribe was arrested and interrogated by the army in 1986 after detectives discovered calls had been made from his carphone to Escobar, leader of the Medellín cartel.

Álvaro Uribe acknowledged that his brother had been arrested but said he had been released and charges were dropped, claiming Jaime was recovering from throat surgery in a local hospital at the time the calls were made. "His car phone was cloned by criminals," Alvaro Uribe tweeted.

The Uribe family has long faced accusations of ties to drug trafficking. A US intelligence report from 1991, declassified in 2004, identified Álvaro Uribe as a "close friend" of Escobar, who was "dedicated to collaboration with the Medellín cartel". It also says Uribe's father was murdered "for his connection with the narcotic (sic) traffickers". Officially Uribe's father died while trying to resist being kidnapped by leftist guerrillas in 1983.

The US state department disavowed the intelligence report when it was published, during Uribe's second year in office, saying it had "no credible information" to substantiate the information.

Another Uribe brother, Santiago, isbeing investigated over the alleged founding and leadership of a rightwing paramilitary group, while Uribe's cousin Mario lost his seat in the senate and was jailed for seven and a half years over ties to paramilitaries, main players in Colombia's drug trade.

• This article was amended on 22 June 2012 because the original said Ana Maria Uribe Cifuentes is awaiting extradition to the US. While her mother, Dolly Cifuentes Villa, is in jail awaiting extradition, Uribe Cifuentes has no charges against her beyond being designated as having links to the Cifuentes Villa clan by the US Treasury. This has been corrected.